So far, the solar storm buffeting Earth is weaker than experts had forecast. But the intensity could grow quickly, perhaps becoming severe, during the next 24 hours if the remainder of the storm strikes the Earth’s magnetic envelope in a particular way, as scientists say it might.

Under those conditions, the storm could pose a more serious threat to power grids, satellites, airliners, and radio communications.

This solar geomagnetic storm – called a coronal mass ejection (CME) by scientists – is the strongest to hit Earth since 2005.

Satellite operators were being advised by NASA-Goddard Space Flight Center in Greenbelt, Md., that some of their systems could be damaged by the cloud of charged particles now reaching earth, which were emitted earlier this week as part a huge solar flare.

Canadian space-weather monitoring groups also sent warnings to power-grid operators at northern latitudes most vulnerable to the storm. At midday, the grid operator for the New England region, which receives the Canadian warnings, said the storm-intensity alerts did not yet require specific actions. Typically, these actions would include firing up local generating plants to reduce stress on long-distance transmission lines.

The nation's three big, regional grids were also doing fine at late morning, according to the North American Electric Reliability Corp., which is in charge of reliability for the nation's major power grids.

Currently, the storm registers at about a G2 level on an intensity scale that goes from one to five, with five being the strongest, says Antti Pulkkinen, a solar weather research scientist at NASA-Goddard.

But that could change. "Based on what we're seeing in the data, it appears there's a good chance of a strong geomagnetic storm somewhere around the G5 level in the next 24 hours," says Dr. Pulkkinen.

Whether this happens could largely be a question of the storm’s orientation.

But if the reverse occurs, which seems possible based on the data he's seeing, "now the fields collide like they love each other, there's and embrace, and energy from the [coronal mass ejection] has opened the gate and floods into Earth's vicinity."

"This is not a bell-ringer yet,” Dr. Baker says. “But it is a storm that looks like it is oriented in a way that should drive it to greater heights."

Intense debate has swirled over and what, if anything, to do about solar storms beyond reactive, defensive actions. Only a handful of such storms has had any serious impact during the past century. Still, societies are more dependent on power grids than ever – and damage to the grid could be severe in some cases.

The power grid is 10 times larger than it was in 1921, when the last solar super storm hit, effectively making it a giant new antenna for geomagnetic current. A far stronger solar outburst could overload and wreck hundreds of crucial high-voltage transformers nationwide, blacking out 130 million people for months and costing as much as $2 trillion, according to a 2010 Oak Ridge National Laboratory study.

The White House and the British government last year unveiled plans to collaborate on a space-weather warning system that would improve predictions. The National Oceanic and Atmospheric Administration (NOAA) is using a computer-modeling system to predict space weather that became operational last fall. The idea is to give power-grid operators and others time and certainty to prepare for a solar storm.

“I think the utility industry has become much more conscious of the threat from geomagnetic storms – and a lot can be done just monitoring the grid and being prepared to lower power on segments of the grid when they need to do it or fire up local generators," says Jeffrey Hughes, director of the Center for Integrated Space Weather Modeling at Boston University, which developed the NOAA computer-modeling system. "Obviously, they don't like to do it because it costs more."